I'm a new forum member and soon I will be the owner of a 70s Fisher Papabear. The seller reconditioned it to as new. But, I would like to discuss the possibility of changing the flue from rear to top. Is this an accepted OK modification?
New Forum Member And New Papabear Owner
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Yes, most welding shops can do that if you don't have the equipment or welding capability. There are threads with the specs of how long the flue pipe should be and how far it projects down into the firebox. This is important for efficiency.
You would definitely want to add an internal baffle with a top vent which is covered extensively in the baffle thread on this Forum.
Yes, most welding shops can do that if you don't have the equipment or welding capability. There are threads with the specs of how long the flue pipe should be and how far it projects down into the firebox. This is important for efficiency.
You would definitely want to add an internal baffle with a top vent which is covered extensively in the baffle thread on this Forum.
I've been reading for the last hour and for the life of me can't find either thread. Maybe a hint of where it is?
Top right corner is a magnifying glass that becomes Search box. (it used to say SEARCH but now is more difficult to find) I used keyword "extend" for my posts on this forum only; Drawings call for 12 Ga pipe 6 inch OD X 5 inches long extending into firebox 3 inches.
Here's one; https://www.hearth.com/talk/threads...ed-mama-bear-to-top-vent.148465/#post-1995191
Here's one; https://www.hearth.com/talk/threads...ed-mama-bear-to-top-vent.148465/#post-1995191
Hey Coaly......... Thanks for the help 
!! I have a mig welder and plasma cutter so as soon as I'm convinced the top flue is the way to go, I'll get on it . Just curious as to wether you'd do the top flue....with 3" into the stove and inside baffle plate...
!! I have a mig welder and plasma cutter so as soon as I'm convinced the top flue is the way to go, I'll get on it . Just curious as to wether you'd do the top flue....with 3" into the stove and inside baffle plate...I would personally find the stove in the configuration I wanted unless it became a time issue or one can't be found locally or reasonable.
The 3 inch extension into the firebox allows the intense heat to build at the stove top so it has to drop before going out. The more times the exhaust changes direction the better - so you don't want flames touching the top and slipping up the flue. I would baffle it with side, rear, or top vent. Baffle size and the square inch area the smoke travels to get out depends on chimney flue diameter and height. Don't weld angle iron inside to set baffle plate on - it's best to keep it adjustable and fine tune it easily for the chimney. In the case of a huge chimney flue you may not be able to baffle it much at all. The baffle adjustment is for the chimney, not the stove.
The 3 inch extension into the firebox allows the intense heat to build at the stove top so it has to drop before going out. The more times the exhaust changes direction the better - so you don't want flames touching the top and slipping up the flue. I would baffle it with side, rear, or top vent. Baffle size and the square inch area the smoke travels to get out depends on chimney flue diameter and height. Don't weld angle iron inside to set baffle plate on - it's best to keep it adjustable and fine tune it easily for the chimney. In the case of a huge chimney flue you may not be able to baffle it much at all. The baffle adjustment is for the chimney, not the stove.
I understand the 3 inches into the stove. But I don't get how to size the baffle based on chimney flue size and height. My clay chimney flue, which is 7" X 7" ID, rises about 30 feet above the stove pipe entrance in the brick wall which is 6 inch round. From the top of the stove to the center of the stove pipe entrance in the brick wall is 25 inches. It has fantastic draw.
Another detail I don't understand is that the original rear flue on the Papabear, not counting that little inside plate on the underside of the flue, never had a baffle such as is recommended on the top flue modification. It seems to me that flames could easily climb inside and up the rear flue as easily as the top flue. So to think out loud, why wasn't the rear flue baffled?
Another detail I don't understand is that the original rear flue on the Papabear, not counting that little inside plate on the underside of the flue, never had a baffle such as is recommended on the top flue modification. It seems to me that flames could easily climb inside and up the rear flue as easily as the top flue. So to think out loud, why wasn't the rear flue baffled?
None of the Bear Series (single door) stoves had baffles. My post above states that I recommend adding a baffle no matter where the flue exits the stove, side, rear or top. The top vent benefits from it the most, but it makes a huge difference with rear or side vented as well. Not as much heat is lost with side and rear vent since more heat is lost straight up than sideways.
When these stoves were built, most were connected to large fireplace flues or larger existing chimneys such as yours. Much more heat is required to be lost up the larger flue to keep the larger area hot. (the larger the diameter and the taller, the more heat required) A factory baffle in these installations would cause rapid creosote formation, so not knowing the chimney it was being connected to, they allowed them to be more inefficient to prevent chimney fires. Had they built efficient stoves requiring 6 inch insulated chimneys, people would have gone to another manufacturer for a stove that would work with their existing chimney. Now manufacturers can say that since they all have to be EPA certified and don't loose enough heat up the stack to heat a larger flue. The key is to keep the flue gas temperature above 250* f. all the way to the top. Below that temperature water vapor from combustion condenses and smoke particles stick to flue walls forming creosote. With the advent of insulated flue liners, the object is to keep the pipe and flue diameter the same size as stove outlet. You have 7X7 or 49 square inch area to keep above 250* all the way up. Heat dissipates into your masonry chimney and if it is an outdoor chimney it is much worse being cooled by outdoor cold air. Some of the heat you loose into the masonry radiates back into the house. Unfortunately a lot rises out through the roof with the masonry mass. Your 6 inch round outlet square inch area on the stove is 28.26 square inches. (the formula pi X radius squared which is a radius of 3 X 3 = 9 X 3.14 = 28.26) That means the exiting hot gasses expand to almost twice the area, cooling as they expand. So you need to loose a lot more heat up the flue to create the same draft you would have with the 6 inch to the top. A larger chimney doesn't draw more, it is only capable of more flow using more heat. It actually has a weaker draft with the same amount of heat lost up it than a smaller diameter flue. Like a larger engine needs more fuel to generate more horsepower, it is only capable of generating more power by adding more fuel. So making your stove the most efficient with a baffle to only allow the heat required for an insulated 6 inch flue that stays hot to the top easily will not work with a less efficient chimney that you have. If you don't line it with 6 inch, you need a smoke space of at least 49 square inches to let much more heat out than a baffle adjusted at 28.26 square inches of space for a smaller flue. The more heat you need to leave out, the less in the building and the less efficient the stove becomes.
Other factors are connector pipe length, number of elbows or horizontal runs, chimney screen. These all add resistance to flow requiring more heat to be left up to maintain the required 250*.
That's why you won't know where to adjust the baffle with all the variables for the highest efficiency until you try a different angle which opens and closes the smoke space. (raise baffle plate at front for smaller space between plate and lower bend - this is where you measure square inch of smoke space) You can not make this smoke space smaller than square inch area of flue.
What makes this very important is the rising gasses in chimney create the low pressure area in stove that allows atmospheric air pressure to PUSH oxygen into the stove. So slowing the draft by cooling flue slows the incoming air which slows the fire.
When these stoves were built, most were connected to large fireplace flues or larger existing chimneys such as yours. Much more heat is required to be lost up the larger flue to keep the larger area hot. (the larger the diameter and the taller, the more heat required) A factory baffle in these installations would cause rapid creosote formation, so not knowing the chimney it was being connected to, they allowed them to be more inefficient to prevent chimney fires. Had they built efficient stoves requiring 6 inch insulated chimneys, people would have gone to another manufacturer for a stove that would work with their existing chimney. Now manufacturers can say that since they all have to be EPA certified and don't loose enough heat up the stack to heat a larger flue. The key is to keep the flue gas temperature above 250* f. all the way to the top. Below that temperature water vapor from combustion condenses and smoke particles stick to flue walls forming creosote. With the advent of insulated flue liners, the object is to keep the pipe and flue diameter the same size as stove outlet. You have 7X7 or 49 square inch area to keep above 250* all the way up. Heat dissipates into your masonry chimney and if it is an outdoor chimney it is much worse being cooled by outdoor cold air. Some of the heat you loose into the masonry radiates back into the house. Unfortunately a lot rises out through the roof with the masonry mass. Your 6 inch round outlet square inch area on the stove is 28.26 square inches. (the formula pi X radius squared which is a radius of 3 X 3 = 9 X 3.14 = 28.26) That means the exiting hot gasses expand to almost twice the area, cooling as they expand. So you need to loose a lot more heat up the flue to create the same draft you would have with the 6 inch to the top. A larger chimney doesn't draw more, it is only capable of more flow using more heat. It actually has a weaker draft with the same amount of heat lost up it than a smaller diameter flue. Like a larger engine needs more fuel to generate more horsepower, it is only capable of generating more power by adding more fuel. So making your stove the most efficient with a baffle to only allow the heat required for an insulated 6 inch flue that stays hot to the top easily will not work with a less efficient chimney that you have. If you don't line it with 6 inch, you need a smoke space of at least 49 square inches to let much more heat out than a baffle adjusted at 28.26 square inches of space for a smaller flue. The more heat you need to leave out, the less in the building and the less efficient the stove becomes.
Other factors are connector pipe length, number of elbows or horizontal runs, chimney screen. These all add resistance to flow requiring more heat to be left up to maintain the required 250*.
That's why you won't know where to adjust the baffle with all the variables for the highest efficiency until you try a different angle which opens and closes the smoke space. (raise baffle plate at front for smaller space between plate and lower bend - this is where you measure square inch of smoke space) You can not make this smoke space smaller than square inch area of flue.
What makes this very important is the rising gasses in chimney create the low pressure area in stove that allows atmospheric air pressure to PUSH oxygen into the stove. So slowing the draft by cooling flue slows the incoming air which slows the fire.
WOW.......Coaly, you sure are an encyclopedia of Fisher Stove information. Your answers to my questions help me understand the operation of Fisher Stoves and I thank you for taking the time to explain to me such a thing.
Well, I was ready to purchase a totally recondition Papabear. But as I was perusing Craigslist I seen listed an original owner selling an unmolested Papabear they had purchased new in approximately 1977. They only seldom used it until around 1980, then they let it sit in the living room as a decoration until this week. Had the original firebrick inside with no cracks. I could use it as is but I think I'll give it a paint job to start its new life with me. I purchased it for $300. What a heavy stove ! Anyway, I'll post pictures soon. I left it on the trailer backed into my garage. It's too heavy to deal with twice in one day.
Well, I was ready to purchase a totally recondition Papabear. But as I was perusing Craigslist I seen listed an original owner selling an unmolested Papabear they had purchased new in approximately 1977. They only seldom used it until around 1980, then they let it sit in the living room as a decoration until this week. Had the original firebrick inside with no cracks. I could use it as is but I think I'll give it a paint job to start its new life with me. I purchased it for $300. What a heavy stove ! Anyway, I'll post pictures soon. I left it on the trailer backed into my garage. It's too heavy to deal with twice in one day.
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The more you understand about the operation the easier it becomes and the more you're going to enjoy the stove.
It's all about how the chimney causes the air to rush into the stove. They are like a car with no engine without a chimney. Any stove will work reasonably well with a good chimney, no stove works well with a poor one. They have to be sized to each other. You can see how a very small chimney on a large stove won't move enough hot gasses upward to create a good vacuum to allow air into the stove. Too large of a chimney on a small stove is very common and requires so much heat the little stove burns hard and doesn't heat the area it's in. People think the stove is the problem. I get a lot of complaints that my "Baby Bear won't heat my cabin!" They try everything imaginable to the stove and neglect the huge fireplace chimney it's connected to because they think the chimney is just there to let the smoke out. Line that big chimney with pipe the same size as stove outlet so it needs less heat left up and the small stove heats the area up fine. Compare it to trying to suck up fluid through a large straw or hose. That is atmospheric pressure pushing the fluid up the straw. It takes a lot of effort removing a lot of air from the larger straw. It takes much less effort using a tiny diameter straw. That's how your stove feels connected to a large diameter chimney.
Sounds like you've got a good one.
The longest lasting paint is Stove Bright and Satin Black is the original color. It's best to paint outside and burn it off with a piece of stove pipe connected before bringing it in. The majority of the smell will be gone and the paint cures with heat, so it won't be very soft to move the stove inside.
I keep them on wheels as much as possible and "walk" them into truck or trailer with planks. Same planks for steps, always lay it on it's side to "walk" up or down ramps. A full set of steps takes a come-a-long to raise or lower. I put a 4 X 4 across doorway and winch away. It's comical when I go to pick one up and the seller says "your going to move this yourself? It took 3 guys to bring it in! Another trick is to put a long 2 X 6 into the rear vent like a handle to pick it up to set on dolly. You can lift them with that long lever or "walk" corner to corner up a ramp easily.
It's all about how the chimney causes the air to rush into the stove. They are like a car with no engine without a chimney. Any stove will work reasonably well with a good chimney, no stove works well with a poor one. They have to be sized to each other. You can see how a very small chimney on a large stove won't move enough hot gasses upward to create a good vacuum to allow air into the stove. Too large of a chimney on a small stove is very common and requires so much heat the little stove burns hard and doesn't heat the area it's in. People think the stove is the problem. I get a lot of complaints that my "Baby Bear won't heat my cabin!" They try everything imaginable to the stove and neglect the huge fireplace chimney it's connected to because they think the chimney is just there to let the smoke out. Line that big chimney with pipe the same size as stove outlet so it needs less heat left up and the small stove heats the area up fine. Compare it to trying to suck up fluid through a large straw or hose. That is atmospheric pressure pushing the fluid up the straw. It takes a lot of effort removing a lot of air from the larger straw. It takes much less effort using a tiny diameter straw. That's how your stove feels connected to a large diameter chimney.
Sounds like you've got a good one.
The longest lasting paint is Stove Bright and Satin Black is the original color. It's best to paint outside and burn it off with a piece of stove pipe connected before bringing it in. The majority of the smell will be gone and the paint cures with heat, so it won't be very soft to move the stove inside.
I keep them on wheels as much as possible and "walk" them into truck or trailer with planks. Same planks for steps, always lay it on it's side to "walk" up or down ramps. A full set of steps takes a come-a-long to raise or lower. I put a 4 X 4 across doorway and winch away. It's comical when I go to pick one up and the seller says "your going to move this yourself? It took 3 guys to bring it in! Another trick is to put a long 2 X 6 into the rear vent like a handle to pick it up to set on dolly. You can lift them with that long lever or "walk" corner to corner up a ramp easily.
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